Sweet potato is one of the most important food crops in our country. According to statistics, sweet potato cultivation and processing in our country rank first in the world, and the total production reaches 85.2 million tons, wherein 55% of it (about 46.86 million tons) turns into industrial raw materials. Sweet potato residue is the plenty of residue produced in the process of processing fresh sweet potato into starch, and is disposed as waste. Therefore, huge renewable resources of biomass have yet been developed and utilized.
Fresh sweet potato generally contains 30% dry matter and 70% moisture. Plenty of waste water containing cell sap is produced in the processing of sweet potato, which is the sweet potato starch waste water. It contains various nutritious organic substances, such as soluble carbohydrates, proteins, vitamins and trace elements. The residue of sweet potato starch processing is analyzed, and the main chemical ingredients are water, starch, crude protein, fiber, fat, etc.
The waste residue of sweet potato produced by finely processing sweet potato to produce starch, vermicelli, instant noodle, starch noodle, etc. accounts for about 10% of the raw materials. The fresh sweet potato residue immediately from the production line generally contains about 90% of the cell sap. Plenty of wet sweet potato residue piles up, and is not effectively developed and utilized. Furthermore, due to the high water holding capacity and swelling capacity of the sweet potato fibers, fresh residue of sweet potato having sugar, nitrogen and various nutritious ingredients contains 90% water, and the chemical oxygen demand (COD) of the waste water thereof >15000 mg/L. Therefore, the residue is susceptible to rancidification caused by fermentation of miscellaneous bacteria, severely pollutes the environment, and leads to huge waste of renewable resources of biomass.
In recent years, the hotspot for developing sweet potato residue includes using acid method, enzymatic method and screening method to remove the majority of starch, protein and fat in the sweet potato residue, to extract dietary fiber and pectin, and prepare them into products. However, the market demand for such products was weak, and they have not been produced in large industrial scales.
The sweet potato residue contains, based on dry weight, more than 50% starch and 22˜26% fiber. The fiber is mainly composed of cellulose, hemicellulose, lignin and pectin, etc., and it is the carbohydrate of thousands of glucose groups in dense structure, which is difficult to be degraded by commercially available cellulase secreted by Trichoderma koningii. The starch produced by pulverizing with a rasping machine and subjecting to a sifting machine is separated. The remaining starch in the sweet potato residue is liquified by α-amylase and saccharified by glucoamylase, and the degradation thereof is not complete. Therefore, it is an important task for performing comprehensive utilization of the waste resources of biomass sweet potato residue, to find a method capable of efficiently transforming sweet potato residue into glucose and developing a new source of sugar, and to industrialize the method. Such non-food source of sugar has significant environmental benefit, social benefit, and economic benefit.